| 摘要 |
A system and method for measuring fluid or gas flow rate, for the system whe re fluid or gas is pumped, such as gas monitoring instrument, via a conduit to a sensor. The flow of gas through a pump (14) is determined by measuring motor back emf which is proportional to motor (12) speed. The motor (12) speed is controlled by pulse width modulation "PWM" control (40) of the motor drive (38) voltage. The back emf is sampled (44) during intervals between the driv e pulses applied to the motor (12). The sampling is done at selected, spaced- apart or infrequent intervals such as ones for every ten or once for every hundred motor drive pulses. In an instrument that uses a microprocessor (56) and analog-to-digital converter (50) to measure gas concentration, the same microprocessor (56) and converter (50) can provide the PWM control of the pu mp (14) in response to back emf generated by the pump motor between the drive pulses. The output of the analog-to-digital converter (50) that correspondin g to the back emf, which in turn corresponds to the pump motor speed is compar ed via microprocessor (56) to set-point value of the desired pumpmotor speed. T he processor then adjusts the PWM to remain the desired motor (12) speed.
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